Handbook of Multimedia for Digital Entertainment and Arts- P19: The advances in computer entertainment, multi-player and online games, technology-enabled art, culture and performance have created a new form of entertainment and art, which attracts and absorbs their participants. The fantastic success of this new field has influenced the development of the new digital entertainment industry and related products and services, which has impacted every aspect of our lives. | 23 Computer Graphics Using Raytracing 539 in a vector form the directions of the reflected and refracted rays can be determined as follows cos 31 N L cos 02 pl - i 2 2 - 1 - cos 0i 2 N reflect 1 C 2N cos 01 14 Vrefract L C cos 01 - cos 02 N 2 2 As an optimization that may be made in the implementation of a raytracer the medium in the absence of geometry may be assumed to have an index of refraction of one. Therefore as 2 is now one the index of refraction for each piece of geometry becomes equal to the ratio of the indices of refraction of the medium to that of its surroundings simplifying 14 to V refract L C cos 01 - cos 02 N 15 Controlling Scene Complexity Because each intersection of a ray with scene geometry may generate additional rays the number of rays to be traced through the scene grows geometrically with the number of ray-geometry intersections and therefore with scene complexity. In extreme cases the number of rays traced and therefore the number of intersection tests performed can reach infinity. Fortunately very few surfaces are perfectly reflective or transparent and absorb some of the light energy falling on them. For this reason the total light energy represented by the secondary rays diminishes with each intersection and the effect of the secondary rays on the output image is less significant with each bound. Note that once a ray escapes the volume enclosing the scene geometry it can no longer generate any ray-geometry intersections and it will not contribute further to the output image. To reduce computational complexity and therefore calculation time required to generate the output image using the raytracing algorithm various methods are usually employed to limit the number of recursions which may be generated by a single primary ray. In its simplest form this can be achieved by placing an upper limit on the number of bounces allowed Shirley 05 . In a more sophisticated system the projected effect of the ray on the output image may be estimated .
